U.S. Pat. Nos. 2,362,777 and 3,123,007 disclose early systems for hydraulically driving a reciprocating well pump, but neither have bearing on the present invention. Many similar patents exist, some having fluid motors for attachment to conventional pumps or to operate a string of sucker rods, which, in turn, operate a conventional downhole pump.
Coberly U.S. Pat. No. 2,952,212 operates by co-mingling spent power fluid with produced liquid from the well, which requires separation and purification fo the power fluid before recirculation to the downhole pump. A later Coberly patent, U.S. Pat. No. 3,005,414, employs a power fluid string and a separate string to return spent power fluid as well as a production string to convey produced liquid to the wellhead.
Of more particular interest are U.S. Pat. Nos. Hammelmann 3,307,484; Garraway 1,448,486 and Sargent 2,748,712; which generally are of the same type as the present invention. However, all three disclose torturous paths or conduits through which hydraulic fluid must flow in order to operate the pump. The conduits, as depicted, are of small cross section relative to the pumps outer diameter and the conduits also have many changes in direction. Such a device can be jammed by a very minor amount of solid, such as will be found in any hydraulic fluid used to operate a downhole well pump, since the fluid cannot be kept as clean as fluid can be kept in a small surface system.
The severest limitation for a downhole device is the limitation of its outer diameter. Such convenient arrangements as outlet pipe 15 depicted in Garraway, or as outlet pipe 4 depicted in Hammelmann, or side outlets 78a as depicted in Sargent, cannot be included in a downhole pump without reducing the abovementioned small flow paths even further, if the pump is to pass downward within typical well tubings.
The small size of the flow paths is even more important when you consider the great increase in pressure drop that is caused by reducing the cross-sectional flow area. Well known laws of hydraulics tell us that given flow rate of a given fluid will produce a pressure drop per unit length of pipe, in direct proportion to the diameter of the flow path raised the fifth power (i.e. should a flow path diameter be reduced to a diameter one third as large, the pressure drop would be increased (3).sup.5, or 243 times the original pressure drop, per unit length, or, perhaps, from 100 psi to 24,300 psi, which would surely render the device impracticable). The importance of providing sufficiently large hydraulic cirucuits that are self-cleaning in downhole hydraulic systems cannot be overstated and it may, therefore, explain substantially the reason that hydraulically-operated downhole pumps have enjoyed less than 1% of the market heretofore, and those few have been of the Coberly type.
In each device of prior art, small conduits must convey fluid to shift the reversing valve before reversal of the pump member can occur. It is, therefore, a primary object of the present invention to provide a dependable and efficient hydraulically-driven downhole pump that does not jam or require excessive pressure to operate.
Another object of the present invention is to provide a reversing valve for a reciprocating pump member which has no conduits necessary for operation, of a flow area smaller than the flow area of the conduit used to convey power fluid to drive the pump.
Still another object of the present invention is to provide a reversing valve for a reciprocating pump member that is shifted by direct action of the power fluid flowing in a conduit used to convey power fluid to drive the pump.
It is also an object of the present invention to provide pressure-aided sealing means to alternately open and close conduits used to convey power fluid to and from the motor chamber.
It is also an object of the present invention to provide means to prevent premature or partial shifting of the reversing valve.
It is also an object of the present invention to provide means to positively, completely and instantaneously shift the reversing valve at the proper time.
It is also an object of the present invention to accomplish such operation of the pump with the least number of moving parts.
It is also an object of the present invention to provide optimum positions of the reversing valve seal members at the instant of hydraulically aided shift.
It is also an object of the present invention to provide suitable inlet valves for the pump chamber so as not to increase the pump outer diameter, but to allow sufficient flow volume to fill the pump chamber for rapid operation of the pump.
It is also an object of the present invention to provide suitable outlet valves for the pump chamber so as not to increase the pump outer diameter, but to allow sufficient flow volume to empty the pump chamber for rapid operation of the pump.
It is also an object of the present invention to provide a suitable valve system such that normal amounts of solids entrained in downhole power fluid and downhole-produced fluid, will not affect the desired operation of the pump adversely.